Off gas firing system



Oct. 18, 1966 F. von WIESENTHAL 3,279,520

OFF GAS FIRING SYSTEM 7 Filed June 12, 1964 Y 2 Sheets-Sheet 1 CAT/ILV37 GENFRA TOE C0 HR G 7 INVENTOR ATTORNEY Pans? vo/v Mesa 221m.

Oct. 18, 1966 P. vow WIESENTHAL 3,279,520

OFF GAS FIRING SYS EM" Filed June 12, 1964 2 Sheets-Sheet 2 I "II EG-I.

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:2; 552 32- 24 2/ I. K) V /7 V 1 INVENTOR PETER v0 PWfJfA/Tl/AL ATTORNEYUnited States Patent 3,279,520 OFF GAS FIRING SYSTEM Peter 7011Wiesenthal, New York, N.Y., assignor to Alcoru Combustion Company, NewYork, N.Y., a corporation of Delaware Filed June 12, 1964, Ser. No.374,686 4 Claims. (Cl. 158-7) This disclosure relates to firing carbonmonoxide in lean concentrations occurring in exhaust from hydrocarbonoatalytic cracking units. The invention contemplates a stack and sealpot arrangement especially suited to this service.

Commercial CO-firing systems must provide not only for the condition offiring but also for the condition when the CO-firing unit is out ofservice for maintenance. In the former condition off gas is fed to theCO-firing unit, and combustion products are vented to the atmosphere viaa stack. The latter condition calls for bypassing the CO-firing unit bydelivering the oflt gas directly to the stack. The present advanceaccommodates both of these conditions in a particularly facile manner byintegrating seal pot construction with fabrication of the stack. Moreparticularly, a stack is fashioned with an inner flue as well as anouter flue mounted about the inner flue. During normal operationproducts of combustion are exhausted to the atmosphere via the outerflue. When the CO-firing unit is out of service and oil gas is to bebypassed around the CO-firing unit, the oif gas is vented via the innerflue. A seal pot mounted in the stack controls flow of the bypass olfgas to the inner flue.

Basically, the arrangement here advanced oifers increased safety,economy and ruggedness over comparable systems. Mounting of the bypassseal pot in the stack gives an added measure of safety in the event ofCO leakage. CO-firing systems are characterized by high temperatures andvelocities as well as wide savings in operating conditions. Seal potsreceive especially sore abuse. Here the bypass seal pot is integratedinto the formidable structure of the stack. Compatibility of the stackstructure with that of the bypass seal pot gives rise to savings.Further, the inner annulus stifiens the stack for greater resistance towind loads and vibrations.

These and other features will appear more fully from the accompanyingdrawing wherein:

FIGURE I is a diagrammatic illustration of the offgas firing system herecontemplated.

FIGURE II is an enlarged elevation in section of the lower portion ofthe stack.

The oii gas firing arrangement set forth herein provides for eitherCO-firing unit 1 being in service or out of service. As best seen inFIGURE I during normal operation feed seal pot 2 can be opened andbypass seal pot 3 can be closed so that 01f gas from catalystregenerator 4 would be fed via feed duct 6 to CO-firing unit 1 where itis burned in a manner well known to petroleum refiners. Usually air andauxiliary fuel are added to the burning oil gas. Heat is recovered fromthe products of combustion by means of non-contact heat exchange with aprocess stream in tube coil 7. Products of combustion exit CO-firingunit 1 by way of exhaust duct 8. These combustion products pass throughexhaust port 9 and are vented through outer flue 11 and outer topopening 12 of stack 13.

When CO-firing unit 1 is not in service, feed seal pot 2 would be closedto prevent off gas from entering CO- firing unit 1 through feed duct 6.Bypass seal pot 3 would be opened so that off gas is shunted to theatmos- 0 phere by way of inner flue 14 and inner top openmg 16. 7

Bypass seal pot 3 is formed integrally with stack 13.

3,279,520 Patented Oct. 18, 1966 Pot 17 with bottom 18 and peripheralshell 19 is connected in sealing engagement about lower end 21 of innerannulus 22. Lower end 21 projects downward into interior 23 of pot 17and is spaced from shell 19 so that bypass chamber 24 is defined betweeninner annulus 22 and shell 19. Bypass duct 26 connects feed duct 6upstream of feed seal pot 2 with bypass chamber 24 above lower end 21 ofinner annulus 22 from whence, when CO-firing unit 1 is not in service,the oil gas can pass under lower end 21 through inner flue 14 and outinner top opening 16.

Bypass seal pot 3 is operated by pool of water 27 so that when the level28 of the water is above lower end 21 a head of water can be maintainedacross the lower end 21 of inner annulus 22.

Off gas is'generally exhausted from catalyst regenerators attemperatures from 800 to 1100 F. Further, carbon monoxide whichcomprises from 3 to 10% of the oil gas is quite lethal. So whenCO-firing unit 1 is to be entered for repair work, it is necessary thatboth feed duct 6 and exhaust duct 8 be positively closed. Positiveclosure is accomplished by means of feed 29 and exhaust 31 guillotinedampers. Feed seal pot 2 must usually be closed in order for feedguillotine damper 29 to be moved into its closed position.

It will be apparent to those skilled in CO firing that wide deviationscan be made in the details of this disclosure without departing from themain theme of invention as set forth in the claims.

What is claimed is:

1. A system for firing off gas from the catalyst regenerator of ahydrocarbon catalytic cracking unit and comprising in combination a feedduct which connects in flow series with the catalyst regenerator toreceive ofi gas therefrom,

a CO-firing unit,

the feed duct connected in flow series with the CO- firing unit todeliver the off gas thereto,

means operatively associated with the CO-firing unit for recovering heatfrom combustion products generated therein,

a feed seal means operatively connected in the feed duct for controllingthe supply of off gas to the CO- firing unit,

a stack with an inner annulus and an outer annulus,

the inner annulus defining an inner flue,

the outer annulus spaced from the inner annulus to define an outer fluetherebetween,

both of the annuli describing top openings so that the inner and outerflues vent to the atmosphere,

means for exhausting combustion products from the CO-firing unit via theouter flue,

a bypass duct connecting the feed duct upstream of the feed seal meansin flow series with the inner flue,

bypass seal means mounted internally of the outer annulus andoperatively associated with the bypass duct for controlling the flow ofoff gas to the inner annulus.

2. A system for firing off gas from the catalyst regenerator of ahydrocarbon catalytic cracking unit and comprising in combination a feedduct which connects in flow series with the catalyst regenerator toreceive 01f gas therefrom,

a CO-firing unit,

the feed duct connected in flow series with the CO- firing unit todeliver the off gas thereto,

means operatively associated with the CO-firing unit for recovering heatfrom combustion products generated therein,

a feed duct connected in flow series with the CO-firing unit to deliverthe off gas thereto,

means operatively associated with theCO-firing unit for recovering heatfrom combustion products generated therein,

a feed seal means operatively connected in the feed duct for controllingthe supply of off gas to the CO-firing unit,

a stack with an inner annulus and an outer annulus,

the inner annulus defining an. inner flue,

the outer annulus spaced from the inner annulus to define an outer fluetherebetween,

both of the annuli describing top openings so that the inner and outerflues vent to the atmosphere,

the outer annulus of the stack defining an exhaust port,

an exhaust duct connecting the CO-firing unit to the outer annulus ofthe stack about the exhaust port for exhausting combustion products tothe outer flue,

a bypass seal pot with a bottom and a peripheral shell connected insealing engagement about the lower end of the inner annulus,

the lower end of the inner annulus projecting downward into the interiorof the bypass seal pot and spaced from the shell so that a bypasschamber is defined between the inner annulus and the shell,

a bypass duct connecting the feed duct upstream of the feed seal meanswith the bypass chamber above 4' the lower end of the inner annulus fromwhence when the CO-firing unit is not in service the off gas can passunder the lower end of the inner annulus to the inner flue, means forintroducing a pool of water into the bypass seal pot whereby when thelevel of the water is above the lower end of the inner annulus a head ofwater can be maintained across the inner annulus. 3. The system of claim2 with meansoperatively connected to the feed duct downstream of thebypass ductforpositive closure of the feed duct,

and means operatively connected to the exhaust duct for positive closurethereof. 4. The system of claim 3 with guillotine dampers providing forpositive closure of the feed duct as well as the exhaust duct.

References Cited by the Examiner UNITED STATES PATENTS 2,777,428 1/1957Campbell et al. 122-4 FREDERICK L. MATTESON, JR., Primary Examiner.

25 E. G. FAVORS, Assistant Examiner.

1. A SYSTEM FOR FIRING OFF GAS FROM THE CATALYST REGENERATOR OF AHYDROCARBON CATALYTIC CRACKING UNIT AND COMPRISING IN COMBINATION A FEEDDUCT WHICH CONNECTS IN FLOW SERIES WITH THE CATALYST REGENERATOR TORECEIVE OFF GAS THEREFROM, A CO-FIRING UNIT, THE FEED DUCT CONNECTED INFLOW SERIES WITH THE COFIRING UNIT TO DELIVER THE OFF GAS THERETO, MEANSOPERATIVELY ASSOCIATED WITH THE CO-FIRING UNIT FOR RECOVERING HEAT FROMCOMBUSTION PRODUCTS GENERATED THEREIN, A FEED SEAL MEAN OPERATIVELYCONNECTED IN THE FEED DUCT FOR CONTROLLONG THE SUPPLY OF OFF GAS TO THECOFIRING UNIT, A STACK WITH AN INNER ANNULUS AND AN OUTER ANNULUS, THEINNER ANNULUS DEFINING AN INNER FLUE,